It belongs, of course, to Arthur Guinness. In our digital age, in a relentless stream of copies and screens, there’s something disarming about such a pure, hand-written piece of history. The founder of Guinness wrote onto these pages on Thursday, January 29th, 1767. And here we, over 260 years later, looking at the same ink and paper. I feel a little tingle travelling through time.

Surprisingly few of Arthur’s original signatures exist, I learn – even the lease on display in the Storehouse is a copy; the original vellum document, which secured a 9,000-year hold on the St James’s Gate site, is carefully stowed in the archives.

"This is just a drop in the ocean,” Eibhlin tells me.

A historian and archivist from Tralee, Co Kerry, she is in her element. Another book, a trove of early 20th century pub labels, could have come from Hogwarts. It harks back to a time when Guinness was still dispatching barrels of porter in barges from the brewery, and pubs bottled and labelled it themselves.

Every document tells a story (see gallery). “If you were to lay out our paper materials end to end, they would stretch about seven kilometres,” she says.

All told, this is the largest private business archive in Ireland. I’ve been allowed a sneak peek as part of a promo campaign for International Stout Day – celebrations are held on the first Thursday of every November, and this year, the Guinness Storehouse is running a festival from November 1-4, with a host of events and tastings including a one-off stout brewed for the occasion.

The Storehouse is Ireland’s most visited tourist attraction, clocking over 1.7m visitors a year. The archives are another story. Materials date back to 1759, but the archives themselves weren’t formally established until 1998, and select materials are accessible by appointment only.

Historians, collectors, Guinness marketers, family history researchers “and anyone with an interest in the Guinness company and brand” is officially welcome - though you need a specific request, and appointments are given in this small room in the Storehouse (as opposed to the climate-controlled storage facilities themselves).

Outside, tourists swirl around the glossy, pint-shaped atrium on their journey through hi-tech displays to a Gravity Bar that will double in size next year as part of a €16m expansion plan. When Eibhlin pulls on her white gloves however, time travels in the opposite direction.

She shows me beautifully written recipe books (no photos allowed… the recipes are proprietorial). There is a hand-painted volume given to Benjamin Lee Guinness by the "Citizens of Dublin" to mark his bankrolling of the restoration of St Patrick’s Cathedral in the 1860s. Other “artefacts” in the collection include barley grains from King Tutankhamun’s tomb.

Around us, cabinets are crammed with vintage glass and stoneware bottles, and Eibhlin has laid out a mouthwatering sample of charcoal drawings – John Gilroy’s drafts of toucans, ostriches and other animals. Guinness brewers and marketers sometimes draw on old labels, recipes and advertising concepts for inspiration, I learn - a modern reboot of its West Indies Porter, for example, saw brewers consult an original recipe from 1801.

In the hallway outside, a small collection of artefacts includes a Guinness fireman’s helmet, draught can ‘widgets’ invented in the 1990s, and the keg from which President Obama’s Guinness was served in Moneygall in 2011.

Guinness wasn’t always a stout, Eibhlin tells me. Arthur’s original brew was an ale – he made what she describes as the “momentous decision” to cease brewing it in 1799 in favour of porter. “Obviously, history has shown that he made the right decision, but it was quite a brave move. There were no other exclusive porter brewers at that stage.”

I’m also amused to learn that the creamy ‘draught’ Guinness, which feels like such a cornerstone of Irish culture, only made its debut in 1959. It was introduced as a 200th anniversary celebration.

That anniversary was also marked by a gob-smacking ‘message in a bottle’ campaign that saw 150,000 specially commissioned bottles filled with scrolls and dumped into the oceans. Anything like it would be an environmental (and PR) scandal today, but the bottles are still washing up around the world.

“Last year, we had a call from a radio station in Nova Scotia,” Eibhlin says. “A lady had been walking on the beach with her daughter, found one and wanted to know a little more about it. So they’re still turning up today…”

The archives are also full of photographs. We browse through black-and-white images of draymen “at tap” (collecting their daily allowance of beer); of enormous “cask pyramids” in the yards, of men loading freight onto Liffey barges; of Victorian master brewers in their pomp.

My over-riding feeling is just how inextricably the history of Guinness is linked with that of Dublin - a fact underscored by its collection of some 20,000 employee records dating from the 1880s to the 1980s.

Eibhlin shows me one original, rolled into a compact bundle like an old newspaper. Key info from these records has by now been extracted and kept in a database, allowing for genealogical queries from direct family members.

“When we started that service, I imagined the interest would mostly come from our American and overseas visitors,” she says. “But it has actually been Irish people themselves.”

After an hour-and-a-half, she closes the last book. From that simple signature in a Brewers’ Guild book to today’s, Diageo-owned, globe-straddling brand, even my short taster tour tells an epic tale.

“It’s not just a record of a beer," Eibhlin says. "It’s a record of all that Guinness was.”

NB:The International Stout Day festival runs from November 1-4 at the Guinness Storehouse (guinness-storehouse.com; from €18pp). For more on the Guinness Archives, visit guinness-storehouse/archives.com.